Did you know about PLC ? About its birth, difference, working principle and structure. If not, don’t miss today’s article of Vietts nh! Many useful things are waiting for you to learn.
Learn PLC
The first thing that customers need to do before choosing a PLC is to learn about them.
What is PLC?
PLC is 1 automation device used a lot in automatic electrical systems of industrial plants.
What does PLC stand for? It stands for the full phrase Programmable logic controller. In other words, we get a programmable controller or a programmable logic controller.
With PLC, users can flexibly use control algorithms logically through programming languages to perform tasks and events according to a certain process.
PLC programming language is very diverse with: C, ladder, State logic, FBD, STL… PLC will rely on received input signals and control algorithms to output output signals to control operation. related machinery and equipment.
Why PLC was born?
In the past, when there was no PLC, to control machines and lines, people had to connect many devices together such as contactors, relays, timers, etc. Depending on the characteristics and requirements of each system, whether the connection is simple or complex. For large systems, technicians have to spend a lot of time connecting and installing equipment. Since 1 device may need to get the signal many times, the number of installations is limited. In addition, the large number of parts and materials will hinder maintenance, repair or maintenance. If there is a problem, finding the fault and retracing the wire will be both costly and time consuming and greatly reduce productivity.
Therefore, people have researched and found appropriate solutions, can work in hazardous places, automate the production process and increase productivity and work efficiency.
And PLC was born in 1968 in the US. At first PLC was quite cumbersome and created many difficulties when controlling equipment, but after many years of changes, PLC improvements have become more compact, more algorithms, and easier to change these algorithms. . Gradually, PLC has more anti-interference ability, high reliability, easy programming language, suitable for many objects. Nowadays, PLCs can exchange communication with control devices, other PLCs, computers, monitoring devices, computers, etc.
What’s the difference between PLCs?
If comparing PLC with computers or microcontrollers, industrial control methods, there are 3 differences:
+ About HMI: To interact with PLC, one needs a human-machine interface or HMI. HMIs have a simple screen, it is used to read text along with keyboards and control panels, quite similar to electronic devices, so it allows users to stop and enter information and PLC.
+ About I/O: I/O will provide information to the CPU and start the pre-programmed process. Depending on the requirements, the user can mix the I/Os together. For PLCs, the CPU will process and store data. Input modules such as switches, sensors, meters and output modules such as lights, motors, valves will connect to the PLC as well as the rest of the machine.
+ The final difference is communication: Not only connecting to input and output devices, PLC also connects to other systems. The purpose is to monitor devices, export data from PLC to SCADA. So it needs ports and some communication protocol to do this.
The superiority of PLC
Of course, in order for PLC to be known and trusted by many people, it is certainly improving gradually in terms of features and benefits. The development of hardware and software along with the advancement of science and technology has helped PLC change with a more compact size, suitable for many complex circuit control tasks. Detail:
+ Ability to work reliably in an industrial environment of production, processing and assembly.
+ PLC programming language is easy to learn and easy to program.
+ Prices are increasingly competitive among models and manufacturers.
+ The design of the PLC is small and light, so it is easy to transport, saving installation space.
+ The structure is not too complicated, so it is quite convenient to repair.
+ With the new PLC, users can expand and upgrade software and hardware parts.
+ PLC communicates easily with HMI devices, laptops, phones and peripherals.
Structure of PLC
Each PLC is divided into 3 main parts:
+ A program memory inside, some models can be extended outside, also called RAM, ROM.
+ CPU processor with the function of handling loaded programs, algorithms, and communication ports
+ Input modules, signal output modules, I/O modules, communication, peripherals.
There are two types on the market today:
+ Simple PLC can be programmed right on the device
+ Complex PLC must be programmed on a computer and connected via Ethernet or USB port.
Working principle of PLC
The operation of the PLC is not too complicated: the PLC will receive the signal from the input device or connected sensors and then based on the parameters that have been programmed initially, process the data and trigger the output. Depending on the job requirements, output and input characteristics, the PLC can automatically start, automatically stop, monitor and record data on machine running time, temperature and productivity during operation. onion. The PLC can also alarm itself if the machine has a problem. PLC is appreciated for its powerful, flexible control capabilities and is suitable for most machine or system applications.
I/O . I/Os
The I/Os listed in the universal list are: weight, analog, digital temperature, high speed.
Signals from switches, buttons, sensors, etc. will be connected to the input module of the PLC. Meanwhile, the actuator will be connected to the output modules. The voltage on the inside of the PLC is 5v, the processing signal is usually 100/240Vac, 12/24Vdc. To be able to notify the status of the modules, the PLC will be equipped with signal lights.
PLC programming
People will program the PLC on the computer first, after completing it, it will be downloaded and put into the controller. Traditional programming languages are usually C. Ladder Logic, Ladder Logic. Those are the two languages commonly used in PLC programming software.
This process will mimic circuit diagrams with logical vibrations being read from left to right. Start with 1 input or more inputs then output. Each step represents a specific action controlled by the PLC. Although there are many programming languages, Ladder Logic is used more because its intuitive nature makes it easier to implement. The C language is a recent innovation. Some manufacturers have specially designed programming software that is available with the purchase of the device.
Advantages and disadvantages of PLC
PLC is also a device, so in addition to its advantages, it inevitably has disadvantages that people need to overcome in the near future.
Advantages of PLC
PLC has many advantages, thuykhidien xin lists some highlights such as:
+ PLC software is easy to understand and use compared to contactless systems, contact systems.
+ PLC programs are easily repaired and changed by the programmer to suit the job requirements, not only with the programs that directly affect the PLC. Some PLCs are also equipped with some additional software to find out hardware and software failures. From there, the work of tracking, replacing or repairing is much more convenient.
+ Because its structure is a contactless switching system, the life of the PLC is slightly longer than that of relay systems with contacts.
+ In terms of reliability of the output signal, the PLC is higher than the signal supplied from the relay controller.
+ PLC will quickly perform control functions unlike computers that are only used as multi-function control tools. The knowledge of PLC repairing or maintaining the system is not too specialized, users only need to learn the basics.
+ With PLC, we can connect the circuit and set up the system easily, inexpensively like controlling the relay when having to connect the circuit, solder the circuit. The setup jobs are stored on disks and tapes, so they can only be copied when needed.
+ PLC connected to CPU by processor and direct connector. The I/O connector will be located between the peripheral device and the CPU. The function of those connectors is to convert the peripheral signal to a logic level or convert the output CPU value from a logic level to a level that the peripheral devices can receive and work with.
+ User can set the area smaller than the relay with contacts.
+ The difference of PLCs compared to computers is: Converting external influences into internal ones is easy. Programs that act internally can become software that parallels and corresponds to external influences.
Disadvantages of PLC
In our opinion, PLC currently has 3 major disadvantages which are:
+ In small-scale machine control circuits, the cost of buying a PLC is certainly much larger than using a relay.
+ Because it is not possible to standardize the PLC programming language worldwide, each manufacturer uses its own language. Therefore, the consistency is limited..
+ New customers approaching for the first time will find it quite difficult to get used to, install, and program.
PLC application in practice
PLC has the richest applications in industries and fields. We can find it in the systems of printers, threading machines, high speed cutting machines, printing machines, spinning machines, packaging machines, in energy monitoring systems, process pumping systems. wastewater, automatic packaging systems, production lines, electrical systems… Today, PLCs are used in factories producing food, pharmaceuticals, garments, textiles, chemicals, and electronic assembly. …
With lines using robotic arms such as boxing, labeling or robots putting materials on conveyors, picking workpieces from the conveyor belt to the table of CNC machines… using PLC is both accurate and fast.
PLC is also used in the product quality inspection line before shipment, the assembly line of electronic components, monitoring the working process of the plating factory..
